1. Field of the Invention
This invention relates in general to hydrocarbon production, and more particularly, to identifying rock types and rock properties in order to improve or enhance drilling operations.
2. Description of the Related Art
Measuring rock properties during drilling in real time can provide the operator the ability to steer a drill bit in the direction of desired hydrocarbon concentrations. In current industrial practice and prior inventions, either resistivity or sonic logging while drilling (LWD) tools are employed to guide the drill bit during horizontal or lateral drilling. The center of these techniques is to calculate the locations of the boundary between the pay zone and the overlying rock (upper boundary), and the boundary between the pay zone and underlying rock at the sensors location. The drill bit is steered or maintained within the pay zone by keeping the drill string, at the sensors position, in the middle, or certain position between the upper and lower boundaries of the pay zone. The conventional borehole acoustic telemetry system, which transmits data at low rate (at about tens bit per second), is employed to transmit the measured data to surface.
Since the sensors are located 30-50 feet behind the drill bit, theses conventional LWD steering tools only provide data used in steering the drill bit 30-50 feet behind the drill bit. As the result, it is only after the 30-50 feet that the operator finds out if the selected drilling path is or is not the desired one. Therefore, these tools are not true real-time tools.
Some newer types of systems attempt to provide data for steering the drill bit, at real-time, while still utilizing conventional borehole telemetry systems (having a relatively slow bit rate). Such systems, for example, are described as including a downhole processor configured to provide downhole on-site processing of acoustic data to interpret the lithologic properties of the rock encountered by the drill bit through comparison of the acoustic energy generated by the drill bit during drilling with predetermined bit characteristics generated by rotating the drill bit in contact with a known rock type. The lithologic properties interpreted via the comparison are then transmitted to the surface via the conventional borehole telemetry system. Although providing data in a reduced form requiring only a bit rate speed, as such systems do not provide raw data real-time which can be used for further analysis, it is nearly impossible to construct additional interpretation models or modify any interpretation models generated by the downhole processor. Further, they require additional and potentially expensive hardware that must be positioned between the drill bit and the drill string.
Some newer types of borehole data transmitting systems utilize a dedicated electronics unit and a segmented broadband cable protected by a reinforced steel cable positioned within the drill pipe to provide a much faster communication capability. Such systems have been employed into conventional LWD tools to enhance the resolution of the logged information. However the modified tools still measures rock properties at the similar location which is 30-50 feet behind the drill bit.
Looking outside the field, some seismic signal technology includes utilization of a vibration sensor positioned on a mud swivel to pick up the seismic signal generated by drill bit drilling the rocks. It is understood, however, that such a position does not provide for sufficient reception of the pilot signal. Another form of seismic signal technology provides a dedicated coupling connector encircling the drill pipe at a location near the mud swivel to carry vibration sensors. The strength of seismic signal may be weakened due to its travelling through the connector to the vibration sensors. Besides requiring the addition of the coupling connector which comprises an annular stator/retaining ring enclosing an insulating rotor, such technology requires the signal to be transferred externally through a combination rotor-stator-brush wiper engagement methodology. Studies have demonstrated that signal accuracy is reduced by this transmission method. Both these two technologies are designed for rotary table type drill rigs which have almost been phased out by a new type of top drive drill rigs.
Accordingly, recognized by the inventor is the need for apparatus, computer readable medium, program code, and methods of identifying rock properties during operational drilling that can be used in real-time steering of the drilling bit during the operational drilling, and more particularly, apparatus specifically designed to fit top drive type drill rigs and having acoustic sensors strategically positioned on the drill rig to maximally pick up the drilling sound which is generated by drill bit biting the rocks (hereafter termed as drilling acoustic signals), a signal transmitting system to transmit signals at high accuracy, and a computer/processor positioned to receive acoustic signals from the acoustic sensors and configured to process the acoustic signals and evaluate lithology type and other petrophysical properties of the rock that is currently in contact with an operationally employed drilling bit, in real-time utilizing acoustic information contained within the acoustic signals and/or evaluated characteristics of the acoustic signals. Also recognized is the need for methods of employing the apparatus.